But then if people only care about the benefits to them, then they'll be overtaken by "lizards" who exploit them but never get voted out because no one thinks voting passes a CBA. Populations who vote "despite" its wastefulness systematically win against those who don't.
Arguably, the only reason any population isn't overrun by lizards is because it's people are mostly "wasteful" in this sense.
One intermediate solution is to force everyone to vote so that it's no longer costly. This is arguably what is accomplished when people promote voting out of civic duty, etc.
But I don't think people are wasteful in that sense. Voter participation and voter awareness tends to be low, at least in the USA. Besides, if your government only works if people act in a specific irrational manner, I don't have high hopes for it, especially considering that one usually cited fundamental role of government is to fix problems where individual rationality does not lead to group rationality.
Forcing people to vote doesn't incentivize people to educate themselves on the issues, which is required to "vote responsibly" according to the usual Western civics class description of how democracy is supposed to work.
Voter participation is very high, and voter decisions very wise, relative to the lizard scenario; and it's not clear that "not being overlorded by lizards" is a kind of irrationality.
Remember, the lizard scenario is something like "500 lizards outvote 300 million and put in 99% tax rates on non-lizards, to be spent entirely on lizards, all because none of the 300 million want to vote, reasoning that their vote doesn't affect the outcome."
Mandatory voting would definitely be an improvement over that for much the same reasons I gave before.
Arguably, the only reason any population isn't overrun by lizards is because it's people are mostly "wasteful" in this sense.
One intermediate solution is to force everyone to vote so that it's no longer costly. This is arguably what is accomplished when people promote voting out of civic duty, etc.